Corneal Metrics Show Risk of Keratoconus Progression After CXL

Girl getting an eye exam at the optician
Happy Latin American girl getting an eye exam at the optician on the phoropter – medical concepts
Changes in Kmax, Kmean, and Ksteep can predict pediatric prognosis after crosslinking.

Most commonly, ophthalmologists rely on 3 corneal metrics to identify progression of keratoconus (KC) in pediatric patients who have already undergone corneal collagen crosslinking (CXL), according to a literature review published in Cornea

“Defining progression is remarkably difficult in KC because typical progression changes (increased corneal elevation, decreased corneal curvature, and a decrease in corneal thickness) often do not coincide within 1 patient,” researchers explain. Compounding this are potential measurement errors, a lack of homogeneity between scanning methods, and variability between observers and technologies, the report adds.

Additionally, KC is more advanced at presentation in children, with a more aggressive course and faster progression than in adults. Therefore, diagnosis and treatment are required at an early stage. Presently, no accepted definition for progression has been established for children. Researchers say the most commonly used topography metrics by which to determine progression are Kmax, Kmean, and Ksteep.

The research team conducted a systematic review of the literature to define the most used criteria for KC progression in children. Their review included 37 studies (2078 eyes). The most common method to report progression was increased Kmax, Kmean, or Ksteep by ≥1.0 D (78.3% of studies). Using these criteria, the mean pooled progression rate after epithelium-off CXL was 9.9% with high heterogeneity between studies (P <.0001).

Investigators note several limitations to their work, including differences among studies regarding the patient’s age, follow-up course, and progression definition, as well as the small sample sizes, different study designs, and variations in therapeutic regimens. In addition, the definition of progression was made according to the most common methods used by the publications themselves, and newer definitions for progression were recently published, which this study did not evaluate. Lastly, some studies on pediatric KC progression after CXL provided only group data, and some did not report any figures on progression. 

“We encourage researchers and clinicians to specifically mention the progression rate in every outcome report to facilitate communication. We suggest using corneal geometric stability based on the mean of 3 measurements as an outcome criterion for progression and encourage including the 1.0 diopter cutoff in the results,” investigators say.


Achiron A, El-Hadad O, Leadbetter D, et al. Progression of pediatric keratoconus after corneal cross-linking. Cornea. July 22, 2021. doi:10.1097/ICO.0000000000002808